Browsing by Subject "Sulfate attack"

Now showing 1 - 5 of 5

Characterization of high-calcium fly ash for evaluating the sulfate resistance of concrete
(2012-05) Kruse, Karla Anne; Ferron, Raissa; Folliard, Kevin J.
Concrete structures are often exposed to sulfates, which are typically found in groundwater and soils, in agricultural run-off, in industrial facilities, and in other source points. These sulfates may attack concrete and significantly shorten the service life of concrete due to reactions between sulfate ions and concrete constituents. These reactions form expansive and deleterious compounds that lead to cracking and spalling of the concrete. This reaction is a function of the sulfate solution but also the physical, chemical, and mineralogical properties of the cement and supplemental cementitious materials (SCMs). It is widely understood that the addition of some fly ashes, by-products of coal combustion power plants, improve the sulfate resistance of the concrete but some fly ash additions actually reduce the sulfate resistance. This project aims to understand this relationship between fly ash and sulfate resistance. Using sulfate testing results on mortar previously obtained at The University of Texas at Austin, this research evaluated the mineralogical, chemical, and physical characteristics of fly ash and attempted to link these measured characteristics (or combinations thereof) to sulfate resistance of concrete.
Durability of calcium-aluminate based binders for rapid repair applications
(2016-05) Lute, Racheal Dawn; Folliard, Kevin J.; Thomas, Michael D.A.; Fowler, David W; Juenger, Maria C.G.; Wheat, Harovel G.
Within the last few decades, the amount of vehicle miles traveled within the US has increased approximately 40% with the construction of new roads only increasing 4% during this same time period. This dramatic increase in traffic on existing infrastructure has led to the rapid decline of the condition our nation’s roads resulting in the increased need for maintenance and repair. Rapid hardening repair materials are in high demand for these applications as they allow for minimal traffic delays and road closures. Calcium aluminate cement (CAC) is a rapid hardening binder that is used for specialty applications where high early strength and increased durability are desired. In recent years, blended cement systems incorporating both CAC and calcium sulfate (C$) with portland cement (PC) have been developed to utilize the rapid hardening characteristics of CAC but at a reduced cost. While the durability of CAC is well researched and documented, the durability of these new blended systems is not yet fully understood. The focus of this research was to evaluate the performance and long term durability of various blended systems which utilize CAC or calcium sulfoaluminate cement (CSA) to attain rapid hardening. More specifically, these systems were evaluated to determine their resistance to common modes of concrete deterioration such as alkali-silica reaction, external sulfate attack, delayed ettringite formation, carbonation, and corrosion in marine environments through in-situ lab methods and large scale outdoor exposure. The results of the testing conducted related to alkali-silica reaction, external sulfate attack, and delayed ettringite formation identified the potential for large levels of expansion in blended systems of PC:CAC:C$ and PC:CSA. Details regarding each mode of deterioration and mechanisms of expansion are discussed.
Durability testing of rapid, cement-based repair materials for transportation structures
(2014-05) Garcia, Anthony Michael; Folliard, Kevin J.; Drimalas, Thanos, 1980-
For repairing concrete transportation infrastructure, such as pavements and bridges, much importance is placed on early-age strength gain as this has a major impact on scheduling and opening to traffic. However, the long-term performance and durability of such repair materials are often not satisfactory, thus resulting in future repairs. This research project focuses on the evaluation of the durability of various rapid-setting cementitious materials. The binders studied in this project include calcium aluminate cement (CAC), calcium sulfoaluminate cement (CSA), Type III portland cement, alkali-activated fly ash (AAFA) , and various prepackaged concrete materials. In addition, selected CAC and CSA mixtures were further modified with the use of a styrene-butadiene latex. The durability aspects studied include freezing-and-thawing damage and the implications of air entrainment in these systems, alkali-silica reaction, sulfate attack, and permeability of the concrete matrix and potential corrosion.
External sulfate attack of concrete : an accelerated test method, mechanisms, and mitigation techniques
(2016-05) Aguayo Jr., Federico Macias; Folliard, Kevin J.; Thomas, Michael D.A.; Fowler, David; Juenger, Maria C.G.; Wheat, Harovel
Sulfate attack of concrete is perhaps the least understood of the major durability mechanisms plaguing reinforced concrete infrastructures. Many studies have attempted to better understand the underlying mechanisms in which the various modes of deterioration by sulfate attack manifest; however, several controversies still exist. Moreover, ASTM C 1012 (2012), which is the most commonly referred standardized laboratory test method to determine sulfate resistance of blended portland cement mixtures, does not always link well to field performance and may take up to 18 months to complete. The research program presented in this dissertation investigates various issues pertaining to the mechanisms, testing methods, and factors influencing external sulfate attack. The primary focus of this research study was to investigate and propose a reliable, and innovative accelerated test method to evaluate the sulfate performance using concrete specimens. The research program was divided into the following four key components: (1) design a method that can obtain results within a reasonable timeframe (less than six months); (2) design a method that uses concrete specimens and thus links more closely to field performance; (3) develop a better understanding on the role and mechanisms of sulfate attack on concrete through a comprehensive research program including field and laboratory investigations; and (4) investigate the use of calcium sulfate (gypsum) used as an additive to mitigate the potential of sulfate attack in blended portland cement mixtures using high-calcium fly ash. The findings in this dissertation led to the development of a potential accelerated test method for determining sulfate resistance by vacuum impregnating concrete (or mortar) samples with sulfate solution to accelerate the ingress and onset of chemical reactions between the hydrated cement paste and sulfate ion (SO42-). The effects of binder type, water-to-cementitious ratio (w/cm), curing regime, sulfate type and concentration are examined. In comparison to the conventional ASTM C 1012 method, results showed a higher rate of expansion with significant distress observed in samples subjected to the accelerated test method and placed in a 5% Na2SO4 solution. Similar trends, but at a relatively lower expansion rate, were also observed in samples placed in a 0.89% Na2SO4 solution. Physical measurements, chemical analysis and microstructural studies were performed periodically on the specimens.
Improving the sulfate resistance of Class C fly ash : a scientific approach to making bad ash concrete
(2018-06-20) Wheeless, Jeremy Oran; Folliard, Kevin J.
Decades of research have shown that high calcium fly ash, when used as a partial replacement for portland cement, produces a binder that is susceptible to external sulfate attack. Previous research studies have shown that the external sulfate attack mechanism affecting these blends can be suppressed by using gypsum as an additive. In this research study, short-term expansion tests, calorimetry, and x-ray diffraction analysis have been used to show how gypsum affects the volumetric stability, hydration kinetics, and early age hydration products that form in these types of binders. Quantifying the hydration products that contribute to the external sulfate attack mechanism and correlating them to the amount of heat produced by the binder is a crucial step to determining the adequate amount of gypsum required to produce sulfate resistant cements containing high calcium fly ash. The use of these investigative techniques may allow for more widespread use of high calcium fly ashes as a replacement of portland cement.